Re: Recursive Routing and Tunnels

From: ALL From_NJ (all.from.nj@gmail.com)
Date: Sun Feb 22 2009 - 21:34:42 ARST

You guys have been really good about adding so much info / detail about
distribute lists and OSPF.

I had forgotten some of this ;-)

Thankfully OSPF spits out a message telling you NO if you try it outbound
... I found out, that it did not work because OSPF told me so. Many thanks
again for all the good info!

I have not heard anything about tunnels and recursive routing, except to try
it again with unnumbered. I have not labbed that up yet, but will
hopefully get an opp tonight.

Can I assume that the method I described (using distribute lists inbound) is
the suggested way? Anything else to solve recursive routing that I should
practice and study? Hoping I am not forgetting anything ...

Many TIA!

Andrew Lee Lissitz

On Sun, Feb 22, 2009 at 3:53 PM, Jason Madsen <madsen.jason@gmail.com>wrote:

> Hi Net,
>
> "distribute-list out" IS allowed under your OSPF process IF your device is
> an ASBR (meaning that your OSPF router is also running another routing
> protocol). I would try your test again, but use an ASBR this time.
> Knowning the nuances of distribute lists is hugely fundamental in lab
> prep'. Although distribute-list out in OSPF isn't really too common, I'd
> make sure you're comfortable with it.
>
> Jason
>
> On Sun, Feb 22, 2009 at 1:47 PM, NET HE <he_net@hotmail.com> wrote:
>
>> Jason,
>>
>> Firstly, I'd like to say thank you for your correcting my understanding.
>>
>> And I labbed it up, to sum it up
>>
>> -OSPF
>> Under ospf process, distribute-list out is not allowed "OUT direction is
>> not allowed in the case of OSPF"
>>
>> -EIGRP
>> Under EIGRP process, distribute-list out followed by routing process such
>> as RIP, static, connected etc, is used to prevent specific routes sourced by
>> the defined routing process from advertising out in EIGRP process
>>
>> -RIP
>> the same as eigrp
>>
>>
>> Best Regards,
>> Net (Xin) He
>>
>>
>>
>>
>> ------------------------------
>> Date: Sun, 22 Feb 2009 12:16:02 -0700
>> Subject: Re: Recursive Routing and Tunnels
>> From: madsen.jason@gmail.com
>> To: he_net@hotmail.com
>> CC: all.from.nj@gmail.com; mcnever@gmail.com; ccielab@groupstudy.com
>>
>>
>> well...yes and no. keep in mind "distribute-list out" in OSPF only works
>> for external routes (E1 or E2). it can be used to prevent the passing of
>> OSPF external routes into another routing protocol / AS, but it can also be
>> used to prevent externally learned routes from going into OSPF. I know, if
>> we want to prevent routes from going "into" OSPF than why not just use
>> distribute-list in? Well, it's just another way to do it. As we all know
>> if there are 5 ways to do a task, it's highly possible that the CCIE lab
>> will tell us we can't use 4 of the ways.
>>
>> if OSPF is learning of the 3.3.3.0/24 route from EIGRP, than you can use
>> "distribute-list 1 out" in your OSPF process on your ASBR to prevent it from
>> entering your OSPF domain. you can use options like " distribute-list 1 out
>> eigrp 100" to specify not only the routes, but which protocol they should be
>> coming / learned from also. You can't specify an interface however like you
>> can with distribute-list in.
>>
>> Jason
>> #23420
>>
>> On Sun, Feb 22, 2009 at 9:28 AM, NET HE <he_net@hotmail.com> wrote:
>>
>> I think the command "distribute-list out" Jason referred to is used to
>> control routes being redistributed into other routing process. For example,
>> redistributing OSPF routes into RIP, you can use either redistribution
>> route-map under RIP process to control routes redistributed into RIP or
>> distribute-list route-map out RIP under OSPF process to control routes
>> redistributed into RIP.
>>
>> Best Regards,
>> Net (Xin) He
>>
>>
>>
>>
>> > Date: Sat, 21 Feb 2009 22:05:22 -0700
>> > Subject: Re: Recursive Routing and Tunnels
>> > From: madsen.jason@gmail.com
>> > To: all.from.nj@gmail.com
>> > CC: mcnever@gmail.com; ccielab@groupstudy.com
>> >
>> > no, the command is distribute list out...not data-base filter. you can
>> do
>> > it on ASBRs for external routes. try it out.
>> >
>> > Jason
>> >
>> > On Sat, Feb 21, 2009 at 10:03 PM, ALL From_NJ <all.from.nj@gmail.com>
>> wrote:
>> >
>> > > Yeah ... I seem to remember something about this distribute list rule
>> ...
>> > > Thanks for mentioning this.
>> > >
>> > > The command:
>> > > ip ospf database-filter all out
>> > >
>> > > This command filters the LSA outgoing, but ... it is not a distribute
>> > > list.
>> > >
>> > >
>> > >
>> > >
>> > > On Sun, Feb 22, 2009 at 12:00 AM, Jason Madsen <
>> madsen.jason@gmail.com>wrote:
>> > >
>> > >> you can do them outbound if you're an ASBR.
>> > >>
>> > >> Jason
>> > >>
>> > >> On Sat, Feb 21, 2009 at 9:56 PM, Jason Morris <mcnever@gmail.com
>> >wrote:
>> > >>
>> > >>> something to keep in mind about how ospf distribute lists work
>> > >>>
>> > >>> you can never do a distribute list OUT with OSPF.
>> > >>>
>> > >>> OSPF filters LSAs from the ospf database to the routing table vs
>> > >>> filtering
>> > >>> routes advertised or recieced from a neightbor like eigrp or rip
>> does.
>> > >>>
>> > >>> all the databases in an area have to have the same info or ospf
>> can't
>> > >>> calculate paths correctly.
>> > >>>
>> > >>> if that makes since.
>> > >>>
>> > >>> jason
>> > >>>
>> > >>>
>> > >>>
>> > >>> On Sat, Feb 21, 2009 at 11:35 PM, ALL From_NJ <
>> all.from.nj@gmail.com>
>> > >>> wrote:
>> > >>>
>> > >>> > Interesting lab testing tonight, was playing w/ tunnel interfaces
>> and
>> > >>> OSPF.
>> > >>> >
>> > >>> >
>> > >>> > I had a scenario I was practicing, basically it was:
>> > >>> >
>> > >>> > NBMA w/ network type of non-broadcast. Can not use neighbor
>> command or
>> > >>> > make
>> > >>> > any config changes to the physical interface on either sides.
>> > >>> >
>> > >>> > So I created a tunnel and added it to OSPF.
>> > >>> >
>> > >>> > As you would expect, recursive routing began to occur.
>> > >>> >
>> > >>> > Here is a nifty debug output which quickly showed why the neighbor
>> > >>> bounces:
>> > >>> >
>> > >>> > R2#debu ip ospf adj
>> > >>> > OSPF adjacency events debugging is on
>> > >>> >
>> > >>> > *Mar 1 04:34:36.531: %TUN-5-RECURDOWN: Tunnel1 temporarily
>> disabled
>> > >>> due to
>> > >>> > recursive routing
>> > >>> > *Mar 1 04:34:37.531: %LINEPROTO-5-UPDOWN: Line protocol on
>> Interface
>> > >>> > Tunnel1, changed state to down
>> > >>> > *Mar 1 04:34:37.531: OSPF: Interface Tunnel1 going Down
>> > >>> >
>> > >>> > I know one answer to solve this is to simply remove the physical
>> link's
>> > >>> > network address from OSPF. Odd learning though, as I tried to
>> > >>> configure
>> > >>> > other method of filters.
>> > >>> >
>> > >>> > OSPF would not take a distribute list OUT for the tunnel interface
>> ...
>> > >>> > figured I would simply keep the local physical link's network from
>> > >>> being
>> > >>> > advertised out via the tunnel. No-go on this.
>> > >>> >
>> > >>> > OSPF did take a Distribute list IN via the tunnel. I denied the
>> local
>> > >>> > link's network ... and all was well in la-la land (where I live).
>> > >>> >
>> > >>> > R1(config-router)#distribute-list 12 in tunnel 1
>> > >>> >
>> > >>> > Would have been easier and quicker for me to simply remove the
>> physical
>> > >>> > link's network from OSPF, but I was / am learning ...
>> > >>> >
>> > >>> > Also, ... I actually prefer a distribute list IN, since if I am
>> able to
>> > >>> > keep
>> > >>> > the physical link's network in OSPF on my hub router, other peers
>> will
>> > >>> > still
>> > >>> > learn about it. I am only filtering via these two routers, and all
>> > >>> other
>> > >>> > routers still learn about the local link's network.
>> > >>> >
>> > >>> > Question for the group:
>> > >>> >
>> > >>> > For recursive learning, any additional thoughts on ways for me to
>> learn
>> > >>> > this
>> > >>> > / explore this / solve this?
>> > >>> >
>> > >>> > I suppose in all of life, the kiss method is the best ... Just
>> figured
>> > >>> I
>> > >>> > would ping yall to see what insights I might learn.
>> > >>> >
>> > >>> > Many TIA,
>> > >>> >
>> > >>> > Andrew Lee Lissitz
>> > >>> >
>> > >>> > --
>> > >>> > Andrew Lee Lissitz
>> > >>> > all.from.nj@gmail.com
>> > >>> >
>> > >>> >
>> > >>> > Blogs and organic groups at http://www.ccie.net
>> > >>> >
>> > >>> >
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>> > > --
>> > > Andrew Lee Lissitz
>> > > all.from.nj@gmail.com
>> >
>> >
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-- 
Andrew Lee Lissitz
all.from.nj@gmail.com

Blogs and organic groups at http://www.ccie.net

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